The present disclosure relates to substrate guided displays including but not limited to head up displays (HUDs), helmet mounted displays (HMDs), wearable displays, near eye displays, head down displays (HDDs), etc.
Substrate guided displays have been proposed which use waveguide technology with diffraction gratings to preserve eye box size while reducing lens size. U.S. Pat. No. 4,309,070 issued to St. Leger Searle and U.S. Pat. No. 4,711,512 issued to Upatnieks disclose head up displays including a waveguide where the pupil of a collimating optical system is effectively expanded by the waveguide. The U.S. patent applications listed in the Cross Reference to Related Applications above disclose compact head up displays (HUDS) and near eye displays using multiple gratings, multiple waveguides, and/or multiple waveguide layers for pupil expansion.
Pupil expansion using multiple layers or multiple waveguides with input and output diffraction gratings adds to the complexity of the waveguide display. For example, pupil expansion using multiple layers, multiple waveguides, and/or multiple gratings can add to the size, weight and cost of the display and can reduce the brightness and contrast of the display. Further, expanding the pupil from a small round collimating lens in two directions using two or more waveguides or using three or more gratings to produce a final expanded pupil can be lossy due to air gaps and the number of gratings. The air gaps can induce geometric coupling losses. Further, expanding the pupil from a small round collimating lens in two directions using two or more waveguides or using three or more gratings to produce a final expanded pupil can add haze to the final image.
Therefore, there is a need for a display with reduced complexity, size, cost, and weight. There is further a need for a compact wearable display that uses diffraction gratings and is not susceptible to haze. Further, there is a need for a compact HUD which uses collimating optics optimized for constrained spaces associated with smaller aircraft. Yet further still, there is also a need for a small volume, lightweight, lower cost waveguide display with less lossiness and haze. Yet further, there is a need for a substrate waveguide near eye display or HUD that requires fewer gratings for pupil expansion. Yet further, there is a need for a wearable display or HMD that requires fewer gratings for pupil expansion. Yet further, there is a need to mitigate solar flare effects associated with waveguide displays.